With a development of a power semiconductor technology, a power of VVVF (Variable Voltage and Variable Frequency) may be relatively easily implemented using a power element capable of high-speed switching. An example of a circuit for generating the VVVF may include a voltage-type inverter which convert a DC voltage as an input to an AC variable voltage as an output.
The voltage-type inverter may be mainly used in energy storage system (ESS), photo-voltaic (PV) inverter, and motor drive technology.
Various pulse width modulation schemes have been developed for an application of such voltage type inverters. The pulse width modulation schemes includes a sinusoidal pulse width modulation (SPWM) and a space vector pulse width modulation (SVPWM). The above SPWM and SVPWM may belong to a continuous pulse width modulation scheme.
A discontinuous pulse width modulation scheme is also used to reduce a switching loss in a power semiconductor. A 60° discontinuous pulse width modulation (DPWM) scheme is the most representative discontinuous pulse width modulation scheme. This discontinuous pulse width modulation scheme may be implemented by appropriately selecting an offset voltage in a pulse width modulation scheme using an offset voltage and a triangular carrier wave comparison PWM.
Alternatively, the discontinuous pulse width modulation scheme may include a discontinuous pulse width modulation scheme of adjusting a discontinuous pulse width modulation period. This scheme may achieve an optimal current total harmonic distortion (THD) and loss at each operating point by freely adjusting a duration of the discontinuous pulse width modulation period. This scheme always has a minimum loss when a power factor is 1. Thus, it is necessary to have a minimum loss regardless of the power factor.